The present invention relates to a medium detecting system used in an apparatus for handling media such as paper media, or the like.
A prior-art medium detecting system has a plurality of optical sensors, each formed of a light-emitting element and a light-receiving element, disposed at various locations in the medium handling apparatus to detect the medium. A variable load resistor is provided in common for the light-receiving elements of a plurality of the sensors. The variable load resistor permits adjustment of its resistance so as to cope with variations in the characteristics of the light-emitting elements and the light-receiving elements, and variations in the percentage of light which is transmitted from the light-emitting elements to the light-receiving elements, due for example to the amount of dust on the light-receiving elements.
This prior-art medium detecting system has the shortcoming that the resistance of the load resistor cannot be adjusted when the medium is not present.
Another problem of the prior art medium detecting system is that the variable resistor has to be manually adjusted.
A further problem of the prior art medium detecting system is that it is not possible to optimize the resistance of the load resistor for each sensor, to cope with variations in the characteristics of the light-emitting elements and the light-receiving elements, variations in the alignment between the light-emitting elements and the light-receiving elements, and variations in the percentage of light which is transmitted from a light-emitting element to its light-receiving element, due for example to the amount of dust on the light-receiving element.